Field of the Invention
This invention relates to illumination and display fields, and in particular, it relates to a wavelength conversion device and related light emitting device.
Description of Related Art
In conventional illumination system or projection system, the light emitting device often employs an excitation light to excite a wavelength conversion material in a wavelength conversion layer to generate a converted light. However, because during the excitation process the wavelength conversion efficiency of the particles of wavelength conversion material cannot be 100%, the lost energy becomes heat, causing heat accumulation and rapid temperature increase of the wavelength conversion material particles, directly impacting the light emission efficiency and useful life of the wavelength conversion material.
A common solution for this problem is that, by using a drive device to drive the wavelength conversion layer to move, the light spot formed by the excitation light on the wavelength conversion layer acts upon the wavelength conversion layer along a predetermined path. This way, the wavelength conversion material in each unit area will not be constantly illuminated by the excitation light, so the heat accumulation in the wavelength conversion material in the unit area is reduced.
However, with the increased demand on the output light power for illumination systems and projection systems, the light power of the excitation light also increases. The higher the light power density of the excitation light, the lower the light emitting efficiency of the wavelength conversion material. When the light power density of the excitation light reaches a certain level, the wavelength conversion material experience a quenching effect, i.e., the light emitting efficiency of the wavelength conversion material decreases dramatically.
Therefore, to ensure high light conversion efficiency of the wavelength conversion material, in conventional technology, the wavelength conversion material layer all operate in an open environment.
Through study and experiments with the conventional technology, the inventors of the present invention discovered that, because of the open operation environment of the wavelength conversion layer, dust can fall on the wavelength conversion layer and optical components (e.g. lens) located near the wavelength conversion layer. Because dust absorbs light well, the adhered dust increases the light energy absorption by the wavelength conversion layer and the optical component. The more the adhered dust, the more the absorbed light energy by the wavelength conversion layer and the optical component. Thus, in the presence of a large amount of dust and when the light power density of the excitation light is high, the wavelength conversion layer and the optical component absorbs a large amount of light every and their surfaces can be burned and become dark, which impacts the light emitting sufficiency of the wavelength conversion layer and shortens the life of the optical component. Therefore, dust prevention and heat dissipation of the wavelength conversion layer are contradictory aspects of the design and cannot be both satisfied.